The invention relates to a low-temperature refrigerator for producing temperatures in a defined low-temperature range, with a cold head which is fitted with a regenerator and in which a thermodynamic circulation process (regenerative cold generation process) is carried out to generate cold. Moreover, the present invention relates to a process for optimising said cold head for a desired temperature range as well as applications.
It is known to employ low-temperature refrigerators in connection with cryogenic pumps or the cooling of magnets in nuclear spin tomographs. In these applications the cold head shall generate temperatures in the range of 20 K or below. Commonly therefore, refrigerators designed to have two or three stages operating according to the Gifford-McMahon.sup.1) principle, for example, are employed in these applications. However, at these low temperatures the refrigerating capacity of these machines is limited. In commercially available two-stage cold heads, the refrigerating capacity amounts to about 5 to 10 W at a temperature of 20 K. If the refrigerating capacity FNT Translator's note: The German text reads "Giffon-McMahon" where "Gifford-McMahon" would be appropriate and in line with the remaining text as well as other publications on this topic. Thus the word "Gifford-McMahon" has been assumed for the translation. requirement is higher, several two-stage cold heads must be employed in order to attain the corresponding refrigerating capacity through the total.